As valuable and important chemical compounds, 1,4-butanediol (BDO) and γ-butyrolactone (GBL) are employed in many industrial and commercial uses. For instance, BDO is an intermediate that is used in common industrial and commercial products, such as polyether diols, urethane polymers, and polyester polymers, or as a plasticizer, a carrier solvent in printing inks, and a cleaning agent. A significant use of GBL is as a chemical intermediate in the manufacture of pyrrolidines. Other uses of GBL, because of its strong solvency properties, include being a stain remover, paint stripper, super-glue remover, or a cleaner for circuit boards in electronics and high technology industry. Other applications include the production of herbicides and as a processing aid in the production of pharmaceuticals.
In conventional industrial synthesis of BDO, as originally developed by Walter Reppe for IG Farben in the 1930s, acetylene reacts with two equivalents of formaldehyde to form 1,4-butanediol, also known as but-2-yne-1,4-diol. Hydrogenation of 1,4-butynediol coverts to 1,4-butanediol. The requirements of handling acetylene meant that for many years only a select few manufacturers could perform the production of BDO. The value of BDO and its derivatives (tetrahydrofuran (THF), GBL, etc.), however, spurred substantial efforts in new process development that resulted in a number of additional processes, including butadiene acetoxylation and allyl alcohol (from propylene oxide) hydroformylation, together with various routes from n-butane via maleic anhydride/maleic acid.
Industrial synthesis of BDO according to the process developed by Davy McKee Ltd., involves conversion of butane-derived maleic acid anhydride via an intermediate methyl ester to BDO. In particular, the Davy process converts maleic anhydride (MAH) to 1,4-butanediol (BDO), tetrahydrofuran (THF) and gamma butyrolactone (GBL) in three process stages. First, molten MAH is mixed with methanol and reacts exothermically to form mono-methyl maleate and using a proprietary acidic resin catalyst, this is converted from mono to dimethyl maleate (DMM). This is hydrogenated to dimethyl succinate (DMS), and then a series of reaction's converts DMS to gamma butyrolactone (GBL) and then to BDO and THF. Finally crude product is refined to market quality BDO and THF by distillation; methanol is recovered for recycle to the MAH esterification stage, with DMS and GBL recovered for recycle to hydrogenation.
In recent years, as interest has grows in moving away from natural gas or petrochemical-derived hydrocarbon sources, manufacturers have concentrated on finding renewable and sustainable “green” material resources. Many have tried to develop a process that marries a biologically-derived hydrocarbon feed source with a system for synthesizing BDO and its associated derivatives, but none have succeeded in doing so. At present, the principal way of making biologically-derived carbon resources has been by means of fermentation to convert sugars and other plant-based carbohydrates into carboxylic acids. The carboxylic acids are more readily transformed into other chemicals. Currently, the carboxylic acids are recovered from fermentation broths as salts instead of as free acids. Several different steps in post-fermentation, downstream processing are required to isolate the free acids, to prepare the carboxylic acids for chemical transformation and to convert the raw acids to useful compounds. These steps have demonstrated various disadvantages, including high cost, generation of significant amounts of byproduct-waste, and limits on economy of scale for easy high-volume production.
Hence, a need exists for a better, more direct method of recovering a variety of carboxylic acids, such as malic or succinic acid, and which can provide a successful route to combine a biologically-derived hydrocarbon source with the production of various products, such as BDO and its derivatives, by means of hydrogenation.